Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $202.73   6.765%   $216.4447   $216.44   $216.45   $216.40  
  Purchase #2 $210.81   5.705%   $222.8367   $222.84   $222.85   $222.80  
  Purchase #3 $55.56   8.697%   $60.3921   $60.39   $60.40   $60.40  
  Purchase #4 $241.71   6.540%   $257.5178   $257.52   $257.50   $257.50  
  Purchase #5 $159.35   9.351%   $174.2508   $174.25   $174.25   $174.30  
  Purchase #6 $191.95   10.782%   $212.646   $212.65   $212.65   $212.60  
  Purchase #7 $211.94   11.278%   $235.8426   $235.84   $235.85   $235.80  
  7 purchase totals = $1,274.05       $1,379.9307   $1,379.93   $1,379.95   $1,379.80